The present application is directed toward power machines. More particularly, the present application is directed toward hydraulic control valve arrangements that provide power signals to work elements such as lift arms. Power machines, for the purposes of this disclosure, include any type of machine that generates power for the purpose of accomplishing a particular task or a variety of tasks. One type of power machine is a work vehicle. Work vehicles are generally self-propelled vehicles that have a work device, such as a lift arm (although some work vehicles can have other work devices) that can be manipulated to perform a work function. Work vehicles include loaders, excavators, utility vehicles, tractors, and trenchers, to name a few examples.
Certain types of power machines with lift arms have hydraulic actuators (often hydraulic cylinders) that selectively provide power to move the lift arm in generally upward or downward directions in response to command signals generated by the operator. In many of these types of power machines, a proportional directional control valve allows hydraulic fluid to enter one end of a cylinder and exit the other end of the cylinder at a rate commanded by the operator. Control valves of this type are normally configured to prevent hydraulic fluid from being introduced into either end of the cylinder when an operator is not generating a command signal.
In some situations, the control valve is configured to allow hydraulic fluid to be evacuated from each end of the actuator, thereby allowing the lift arm to be controlled by gravity, with only engagement of an uneven terrain by an implement attached to the lift arm to allow the lift arm to be raised over a lowered position. Such a condition is known as a float condition, in that the lift arm is allowed to float up and down relative to the frame of the machine without any power, often in the form of pressurized hydraulic fluid, being provided to the actuator.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.